Hydraulic Circuit
A hydraulic circuit is the power transmission chain that delivers the flow produced by a pump through valves to a cylinder or hydraulic motor and returns the oil to tank; because the oil returns to the tank and not to the pump, this arrangement is called an open circuit. On mobile equipment typical working pressure is 150-250 bar and pump flow rate is in the 20-80 l/min range. The pump determines flow rate; the load determines pressure.
Splitting the circuit into five elements makes your job easier when hunting for a fault:
- Pump: produces the flow rate. If the volume it sweeps per revolution is fixed, flow rate depends on engine speed.
- Directional control valve: selects which port the flow goes to.
- Actuator: a cylinder produces linear force, a hydraulic motor produces rotary force.
- Safety and control components: relief valve, check valve, throttle valve.
- Tank and filters: stores the oil, separates air, sheds heat.
The practical benefit of this split is this: if a movement has slowed down the problem is on the flow rate side (pump wear, a restricted line); if force is insufficient it is on the pressure side (relief valve setting, internal leakage). AXI's manual lever retrofit kits stand outside this circuit: HCT400 and HCT402 move the valve's control lever from the outside and do not touch the oil, the hoses, or the inside of the valve. The vehicle therefore continues to determine the pressure and flow rate of the circuit; the kit only manages remotely how far the lever is opened.
Where this term is used: What Is a Hydraulic Lever Retrofit Kit? Definition, Components, Operating Principle